The present invention relates to a technique for stiffening hats, particularly wool felt hats, and to compositions therefor.
In the manufacture of hats, particularly felt hats made from wool and/or fur, it is customary to add a stiffening agent to the material forming the hat to give the ultimate hat product appropriate stiffness as well as water resistance. In the past, a number of different naturally occurring resins have been used for this purpose. For example, animal glue, gelatin, tragacanth, shellac and various natural gums such as gum arabic have been used. Also tried were some oils such as linseed oil. Of these materials, shellac seems to exhibit the best combination of properties, and accordingly shellac has been the material of choice for the last 125 years.
In a typical hat-manufacturing process, clean wool fibers are first defatted by treatment with ethylene chloride, chloroform, or any solvent that will remove grease and oils, and then assembled into a web or batt of predetermined thickness. The batt is then washed with hot water to shrink and interlock the fibers (felting) and thereby provide some mechanical stability to the hat body.
Next, the batt is dyed or otherwise processed to develop the desired color. Inasmuch as wool is naturally acidic in nature, acidic dyes are typically used for this purpose. In the case of white hats, optical brighteners and in some instances small amounts of blueing are also added. Typically, the dyeing, brightening and/or other coloring operation is accomplished at a pH of about 2.5 to 3.5, the target being approximately pH 3.0.
Once the coloring operation is complete, the felted body is impregnated with a stiffening agent. In the case of shellac, this is usually done with the shellac being in the form of aqueous emulsion. Although shellac is readily soluble in alcohol, it is preferable to avoid organic solvents in the hat-stiffening process for safety reasons. Moreover, although shellac is also soluble in highly alkaline water, highly alkaline conditions would adversely affect the chemistry of the dyes, etc. used in the acidic coloring process. Therefore, alkaline conditions (pH above 7) also are typically avoided. Accordingly, it is conventional to employ shellac emulsified in water using borax (sodium borate) and/or sodium perborate as the emulsifier agent as this will provide an impregnating composition which is essentially free of alcohol or other organic solvent and also exhibits an essentially neutral pH, i.e., about pH 6.4 to 6.8, only slightly on the acidic side.
After impregnation, the body is worked into the desired shape and stiffened. Usually, this is done by first forming the body into the desired shape on a suitable mold and then subjecting the so formed body to heat and pressure to "set" the stiffening agent therein and thereby fix the shape of the hat permanently into the body. Permanently fixing the shape of the body into the desired shape by heat and pressure is known in the art as "blocking" or "proofing" and is typically done two or three times in most hat forming processes. As a result, a precursor hat product having substantially the desired size and shape is typically produced.
In order to produce a final hat product, the hat precursor produced as described above is typically trimmed to size and then subjected to "beating," i.e., vigorous working to make the product more supple. Finally, the beaten product may be subjected to a final stiffening step with heat and pressure, if desired. Depending on the desired appearance of the final product, the so-formed hat may also be subjected to "pouncing," i.e., sanding to remove external long fibers.
Shellac has been the material of choice for hat stiffening for the last 125 years because it exhibits the right combination of properties. When dispersed in aqueous phase, it shows good wetting properties and hence good affinity to wool and fur fibers during impregnation. In addition, it flows easily during repeated blocking steps after precipitation with the acid in the body and thereby is easy to use in the hat molding/shaping operation. It also exhibits a suitable amount of adhesiveness and flexibility and thereby provides the appropriate amount of stiffness to the final hat product. It is compatible with acidic dye systems so that it can be used with conventional dyes without difficulty, and finally it also exhibits low odor and is therefore not unpleasant to use.
However, shellac is a naturally-occurring product. As a result, it is normally subject to significant variations in both price and availability.
For this reason, efforts have continued over the last 50 years to find a substitute for shellac to avoid these difficulties. Significant work has been centered on replacing shellac with synthetic resins such as polyvinyl acetate, polyvinyl alcohols, polyvinyl chloride and the like. However, to date, a suitable replacement for shellac has not yet been found.
Accordingly, it is an object of the present invention to provide a new composition for use in stiffening hats, particularly felt and fur hats, which exhibits the same excellent combination of properties as shellac but which is based on synthetic resin instead of naturally occurring substances.